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RAPAPORT... Stornoway Diamond Corporation optimized its plant design for the Renard diamond project in order to add large diamond recovery capacity early in the project. In January 2013, the plant's optimized feasibility study contemplated a diamond plant flow-sheet geared to recover diamonds up to 30mm in diameter (equivalent to a 200-carat round octahedral stone), leaving room to retrofit a large recovery capacity later, and a cost estimate of about $148 million (CAD 163 million), excluding capitalized operating costs. But with new modifications made recently, the plant design will recover diamonds up to 45mm in diameter (equivalent to a 600-carat round octahedral stone), with a corresponding capital cost estimate of $130 million (CAD 147.1 million).
Stornoway expects to pour concrete for the plant’s foundation in April, but continues to review design efficiencies in order to achieve cost savings. Matt Manson, the president and CEO of Stornoway, said, "These plant design optimizations that we will implement at Renard will allow us to recover the potential value upside from large diamonds that is a characteristic feature of the project. The most recent valuation of Renard’s diamond samples, conducted in March 2014 by WWW International Diamond Consultants Ltd., indicated a weighted average of value of $190 per carat for the three kimberlites in the project’s mineral reserve, and $197 per carat for Renard 2, which represents 82 percent of production in the first 11 years. These valuations, being unescalated base-case diamond price models developed in the conventional manner, assume only nominal value from diamonds larger than 10.8 carats in size. However, the size distribution of samples collected at Renard 2 suggest the potential to recover approximately three to six stones between 50 carat and 100 carat in size, and one to two stones greater than 100 carat in size, every 100,000 carats (representing two to three weeks of output at full production)."
The optimized Renard diamond plant flow sheet will maintain the three-stage crushing regime that was established in the January 2013 study. Run-of-mine ore will be broken down with a primary jaw crusher, utilizing a 230mm top size cut-off and fed to a 4 meter diameter rotary scrubber for disaggregation. Direct feed to dense media separation (DMS) circuits will be +1mm to -19mm (compared with +1mm to -30mm, previously), so as to improve efficiency and reduce diamond breakage risk, according to Mason.
Stornoway anticipates that diamond recovery from concentrate will be conducted through magnetic separation and X-ray technology with no grease table. Already, bench tests on Renard diamonds suggested a 98 percent recovery efficiency with the X-ray sorters, the mining company stated. Direct feed from the scrubber product screen to the large diamond recovery circuit will be +19mm to -45mm, with the top size cut-off adjustable to 60mm. Oversize material between +45mm and -230mm will fed to a cone-crusher under choke feed, before returning to the DMS and large diamond recovery circuits by way of a sizing screen. The non-diamond bearing material from the large diamond recovery circuit and the DMS tails between +6mm and -19mm will be conveyed to a high pressure grinding rolls, with the resulting cake returning to the scrubber for disagglomeration, Stornoway explained. Fine tails at -1mm will be recovered through a thickener and degrit cyclone before dewatering by centrifuge and combination with the +1mm -6mm DMS tails for disposal by dry-stacking.
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